Field of the Invention
The present invention relates to an image forming apparatus and an image forming method.
Description of the Related Art
An ink comprising pigment is known for use in ink-let printing. However, when applied to a recording medium, the ink comprising pigment does not penetrate to the inside of the recording medium and tends to remain at the surface of the recording medium.
In an image printed from an ink comprising pigment, there are often areas of different degrees of glossiness. In other words, there will be a relatively glossy area where the glossiness is conspicuous and a relatively matte area where the glossiness is not observed within the image. This difference of degree of glossiness between areas in a printed image is recognized as “unevenness of the glossiness.” The problem of unevenness of the glossiness is particularly relevant for photograph picture quality.
Some methods to solve the problem have been suggested, including providing an overcoat of colorless transparent clear ink to an image produced from an ink comprising pigment. For example, in Japanese Patent Laid-Open No. 2004-306557, a method to improve glossiness is disclosed where clear ink is provided to the non-printing area and the low duty area of the recording medium.
Furthermore, in addition to obtaining printed images with high degree of glossiness, it is desirable to control the degree of glossiness depending on a preference of the user. In other words, there is a need for an apparatus which prints an image with a desired degree of glossiness in certain portions, and relatively lesser or greater degree of glossiness in other portions by coordinating a method of applying clear ink to the recording medium. US 2005/0156964 discloses a method including printing a test pattern of a clear ink on a print medium and determining an application amount of the clear ink based on the glossiness of the printed test pattern.
In addition, Japanese Patent Laid-Open No. 2012-49719 discloses a method for reducing interference of colors when a clear ink is used by using more than two kinds of clear ink and applying a randomly set amount of clear ink to each of the pixels of a image.
However, the methods described in the above-mentioned documents do not sufficiently limit unevenness of the glossiness while allowing for control of the degree of glossiness.
FIGS. 1A and 1B are schematic views of a printed image demonstrating why known recording methods do not sufficiently limit unevenness of the glossiness and allow for controlling of the degree of glossiness.
Each divided area in FIGS. 1A and 1B represent one pixel in a printed image, including pixels 1 where only clear ink was applied, pixels 2 where only a pigmented ink was applied, pixels 3 where both the clear ink and the pigmented ink were applied, and pixels 4 where neither the clear ink nor the pigmented ink were applied. In addition, while FIGS. 1A and 1B illustrate the pixels schematically as non-overlapping rectangular shapes, it should be understood that in practice, the ink dot is generally in the shape of a circle, and adjacent ink dots may overlap.
In US 2005/0156964, the glossiness is controlled with one kind of clear ink. As shown in FIG. 1A, when clear ink was applied to the pixels 1 where a pigmented ink was applied and also applied to pixels 3 where the pigmented ink was not applied, the surface of the printed matter is completely covered by the clear ink. As a result, generally comparatively uniform glossiness is provided. However, the degree of surface glossiness of the printed matter barely changes even if additional clear ink is applied thereon. On the other hand, decreasing the amount of clear ink causes a decrease in coverage by the clear ink such that the pigmented ink and the print medium are exposed as shown by pixels 2, 4 in FIG. 1B. Because the degree of glossiness is different among clear inks, pigmented inks, and recording mediums, unevenness of degree of glossiness occurs in the printed matter. In other words, the limiting of the unevenness of the glossiness together with the ability to control of the degree of glossiness was not sufficiently achieved by the US 2005/0156964.
In addition, Japanese Patent Laid-Open No. 2012-49719 discloses a method for reducing interference of colors when a clear ink is used by using more than two kinds of clear ink and applying the clear inks to each of a plurality of pixels with a randomly set amount of the clear inks for each of the pixels. But, Japanese Patent Laid-Open No. 2012-49719 does not disclose control of the degree of glossiness as a user desires.